Improved materials are required for the fabrication of high quality, liquid crystal, pictorial display panels. Materials have been sought which, when added to nematic liquid crystal mixtures, impart longer operational lifetimes, provide faster response times, increase the reflectivity of scattering displays, exhibit higher contrast ratios with minimum background scattering, show wider gray scale ranges preferably with a low voltage threshold for dynamic scattering mode (DSM) activation and increase the operational temperature range of the liquid crystal mixtures.
For field effect display devices, liquid crystal mixtures exhibiting a low viscosity and a high negative dielectric anisotropy as well as high birefringence are sought. The increased birefringence and low viscosity will allow construction of thinner and thus faster responding devices. As the negative dielectric anisotropy increases in its absolute value, the threshold voltage of a field-effect device decreases which correspondingly contributes to faster responding devices as well as longer operating lives.
Certain dopants have been employed to increase the positive dielectric anisotropy of liquid crystal mixtures utilized in field-effect devices such as watches. However, this technique has not been too successful for use in field-effect devices requiring a negative dielectric anisotropy.